1. Field of the Invention
The present invention relates to systems and methods for transmitting and/or receiving electromagnetic signals, and in particular to a circularly polarized antenna having an improved axial ratio characteristic.
2. Description of the Related Art
Circularly polarized antennas are used in a variety of applications, including communications between vehicles with metallic structures such as aircraft and spacecraft, and terrestrial assets. Circular polarization is also used in satellite communication antennas because it allows the receiver on the ground to be in any orientation with respect to the satellite without incurring polarization mismatch. It also allows twice the data rate to be used sent using the same bandwidth, because two different data streams can be sent on left and right hand circular polarization.
However, for effective transmission and reception of such circularly polarized signals, the antennas on both the satellite and the ground or air station must have low axial ratio (ratio of the major axis to the minor axis of the polarization ellipse), in order to preserve the polarization purity between the two components (left and right hand polarizations), and minimize interference between the two.
What is needed is a circularly polarized antenna that provides a low axial ratio. The present invention satisfies that need.